ABSTRACT
This chapter is exclusively dedicated to explaining the origin, and to analyze the propagation and the effects of Very fast transients (VFT) in Gas Insulated Substations (GIS). VFT within a GIS are usually generated by disconnect switch operations, although other events, such as the closing of a grounding switch or a fault, can also cause VFT. VFT in GIS can be divided into internal and external. Internal transients can produce overvoltage between the inner conductor and the enclosure, while external transients can cause stress on secondary and adjacent equipment. VFT caused by switching operations and faults can produce high-frequency electromagnetic interference, which can couple into lower voltage control circuits and electronic equipment, and cause some stress. The level reached by VFT overvoltage originated by disconnector switching or line-to-ground faults inside a GIS is in general the basic impulse insulation level of substation and external equipment.
